mysql实现sequence功能的代码

mysql实现sequence功能

1.建立sequence记录表

  CREATE TABLE `sys_sequence` (   `seq_name` varchar(50) CHARACTER SET latin1 COLLATE latin1_bin NOT NULL,   `min_value` int(11) NOT NULL,   `max_value` int(11) NOT NULL,   `current_value` int(11) NOT NULL,   `increment_value` int(11) NOT NULL DEFAULT '1',   PRIMARY KEY (`seq_name`)  ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

 2.建立sequence基础函数

  DELIMITER $$  CREATE DEFINER=`root`@`%` FUNCTION `_nextval`(name varchar(50)) RETURNS int(11)  begin   declare _cur int;  declare _maxvalue int; -- 接收最大值  declare _increment int; -- 接收增长步数  set _increment = (select increment_value from sys_sequence where seq_name = name);  set _maxvalue = (select max_value from sys_sequence where seq_name = name);  set _cur = (select current_value from sys_sequence where seq_name = name);   update sys_sequence           -- 更新当前值  set current_value = _cur + increment_value   where seq_name = name ;   if(_cur + _increment >= _maxvalue) then -- 判断是都达到最大值     update sys_sequence       set current_value = min_value       where seq_name = name ;  end if;  return _cur;   end$$  DELIMITER ;

3.插入想要建立的sequence

  INSERT INTO `mydb`.`sys_sequence`  (`seq_name`,  `min_value`,  `max_value`,  `current_value`,  `increment_value`)  VALUES  ('seq_name1', 1, 99999999, 1, 1);

4.使用sequence

  select _nextval('seq_name1');